Image correction circuit, image correction method and image display

ABSTRACT

An image correction circuit includes: a region determining means for determining an intermediate luminance region in each image frame on the basis of the description of input image data; a luminance distribution acquiring means for acquiring a luminance distribution of input image data in the determined intermediate luminance region in each image frame; a determining means for determining an input/output characteristic line in each image frame by adaptively changing a predetermined reference input/output characteristic line on the basis of the acquired luminance distribution of the intermediate luminance region, the input/output characteristic line defining the substance of image correction on input image data; and a correction executing means for executing image correction on input image data on the basis of the determined input/output characteristic line.

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese PatentApplication JP 2006-138165 filed in the Japanese Patent Office on May17, 2006, the entire contents of which being incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image correction circuit having afunction of performing a correction process on an image signal, an imagecorrection method and an image display.

2. Description of the Related Art

Apparatuses such as television receivers, VTRs (Video Tape Recorders),digital cameras, television cameras or printers typically have an imageprocessing function which makes image quality correction to an inputimage, and then outputs the input image (for example, functions such asluminance or contrast control, and contour correction). Such a functionis effectively applied mainly to a totally dark and low-contrast imageor a blurred image.

Among these functions, in general, the contrast control is performed bycorrecting a gamma curve which represents so-called gammacharacteristics, and as an example, there is a method of using aluminance distribution as the histogram distribution of an input image.More specifically, for example, as shown in FIG. 13A, in the case wherea luminance distribution (a luminance distribution 106A) is distributedin a low luminance region (a black level region), for example, as shownin FIG. 13B, a gamma curve is corrected from L101 to L102. Likewise, forexample, as shown in FIG. 14A, in the case where a luminancedistribution (a luminance distribution 106B) is distributed in a highluminance region (a white level region), for example, as shown in FIG.14B, a gamma curve is corrected from L101 to L103, and, for example, asshown in FIG. 15A, in the case where a luminance distribution (aluminance distribution 106C) is distributed in an intermediate luminanceregion, for example, as shown in FIG. 15B, a gamma curve is correctedfrom L101 to L104. In addition, the amount of correction which is set ateach luminance level at the time of correcting the gamma curve is calledgain.

Moreover, for example, in Japanese Unexamined Patent ApplicationPublication Nos. 2006-93753 and 2005-175933, there are disclosedcontrast improvement methods in which the luminance distribution of aninput image is detected as a histogram distribution, and a gamma curveis corrected at each distribution peak on the basis of the luminancehistogram distribution.

SUMMARY OF THE INVENTION

In contrast improvement methods using a luminance histogram distributionin related arts, as shown in FIGS. 11A and 11B through 13A and 13B,distribution results detected in all luminance regions are reflected tocontrast improvement in all luminance regions, or as shown in JapaneseUnexamined Patent Application Publication Nos. 2006-93753 and2005-175933, a distribution result detected in a part of a luminanceregion is reflected to contrast improvement in the part, and a luminanceregion where a luminance histogram distribution is detected is apredetermined fixed region. However, in the case of such contrastimprovement methods, for example, as will be described below, dependingon the descriptions of an input image, the contrast may not be improvedeffectively, or a displayed image may appear unnatural.

In other words, for example, it is considered that in the case whereonly one distribution peak or a small number of distribution peaks existin a luminance histogram distribution in an image frame, when a gammacurve is corrected at each distribution peak detected in a fixedluminance region, effective contrast improvement can be achieved.However, in the case where a large number of distribution peaks exist ina luminance histogram distribution, when a gamma curve is corrected ateach of such a large number of distribution peaks on the basis of adistribution result in a fixed luminance region, for example, the gammacurve are complicated like gamma curves L105A and L105B shown in FIGS.16A and 16B. Therefore, for example, as shown in FIG. 16A, the effect ofimproving contrast is reduced, and when the slope of a curve isincreased to enhance the effect, for example, the curve has a negativeslope like the gamma curve L105B as shown in FIG. 16B, thereby adisplayed image appears unnatural.

Thus, in techniques in related arts in which the distribution resultdetected in the predetermined fixed luminance region is reflected tocontrast improvement, it is difficult to effectively improve contrastirrespective of the descriptions of an input image.

In view of the foregoing, it is desirable to provide an image correctioncircuit capable of achieving effective contrast improvement irrespectiveof the descriptions of an input image, an image correction method and animage display.

According to an embodiment of the invention, there is provided an imagecorrection circuit including: a region determining means for determiningan intermediate luminance region in each image frame on the basis of thedescriptions of input image data; a luminance distribution acquiringmeans for acquiring a luminance distribution of input image data in thedetermined intermediate luminance region in each image frame; adetermining means for determining an input/output characteristic line ineach image frame by adaptively changing a predetermined referenceinput/output characteristic line on the basis of the acquired luminancedistribution of the intermediate luminance region, the input/outputcharacteristic line defining the substance of image correction on inputimage data; and a correction executing means for executing imagecorrection on input image data on the basis of the determinedinput/output characteristic line. In this case, “a referenceinput/output characteristic line” is not limited to the characteristicof a line shape, and may be a characteristic line shown by a curve.

According to an embodiment of the invention, there is provided an imagecorrection method including the steps of: determining an intermediateluminance region in each image frame on the basis of the descriptions ofinput image data; acquiring a luminance distribution of input image datain the determined intermediate luminance region in each image frame;determining an input/output characteristic line in each image frame byadaptively changing a predetermined reference input/outputcharacteristic line on the basis of the acquired luminance distributionof the intermediate luminance region, the input/output characteristicline defining the substance of image correction on input image data; andexecuting image correction on input image data on the basis of thedetermined input/output characteristic line.

According to an embodiment of the invention, there is provided an imagedisplay including: a region determining means for determining anintermediate luminance region in each image frame on the basis of thedescriptions of input image data; a luminance distribution acquiringmeans for acquiring a luminance distribution of input image data in thedetermined intermediate luminance region in each image frame; adetermining means for determining an input/output characteristic line ineach image frame by adaptively changing a predetermined referenceinput/output characteristic line on the basis of the acquired luminancedistribution of the intermediate luminance region, the input/outputcharacteristic line defining the substance of image correction on inputimage data; a correction executing means for executing image correctionon input image data on the basis of the determined input/outputcharacteristic line, and a display means for displaying an image on thebasis of input image data on which image correction is performed.

In the image correction circuit, the image correction method and theimage display according to the embodiment of the invention, theintermediate luminance region is determined in each image frame on thebasis of the descriptions of input image data, and a luminancedistribution of input image data in the intermediate luminance region isacquired in each image frame. Moreover, the reference input/outputcharacteristic line is adaptively changed on the basis of the acquiredluminance distribution of the intermediate luminance region, thereby theinput/output characteristic line is determined in each image frame.Then, on the basis of the determined input/output characteristic line,image correction on input image data is executed. Therefore, theinput/output characteristic line is determined on the basis of theluminance distribution in the intermediate luminance region in eachimage frame on the basis of the descriptions of input image data, so theinput/output characteristic line easily forms a simple curveirrespective of the descriptions of input image data.

In the image correction circuit according to the embodiment of theinvention, the above-described region determining means can have aconfiguration so as to determine a weighed luminance center of aluminance distribution of input image data in each image frame, and todetermine, as the above-described intermediate luminance region, an areadetermined by setting a first width from the acquired weighed luminancecenter to a low luminance side and by setting a second width from theweighed luminance center to a high luminance side. In this case, “aweighed luminance center” means a luminance position corresponding to avalue equal to the sum of the product of luminance and frequency (totalintegral) divided by the sum of frequency in a luminance distribution ofone image frame.

The image correction circuit according to the embodiment of theinvention can have such a configuration that the above-describedluminance distribution acquiring means acquires a black-sideintermediate luminance distribution in each image frame as a luminancedistribution in a region between a lowest luminance in the determinedintermediate luminance region and a reference luminance provided in thecenter of the intermediate luminance region, and the above-describeddetermining means determines a low-luminance-region input/outputcharacteristic curve on the basis of the acquired black-sideintermediate luminance distribution, the low-luminance-regioninput/output characteristic curve passing through a reference point, inthe reference input/output characteristic line, determined in accordancewith the reference luminance and through a minimum luminance point ofthe reference input/output characteristic line, and the above-describedcorrection executing means executes image correction on input image datahaving a luminance lower than the reference luminance on the basis ofthe determined low-luminance-region input/output characteristic curve.In such a configuration, the low-luminance-region input/outputcharacteristic curve as a part of the above-described input/outputcharacteristic line easily forms a simple curve irrespective of thedescriptions of input image data.

In this case, it is preferable that the above-described luminancedistribution acquiring means further acquires a white-side luminancedistribution as a luminance distribution in a region between a highestluminance in the determined intermediate luminance region and therefrence luminance, the above-described determining means furtherdetermines a high-luminance-region input/output characteristic curvepassing through the reference point, in the reference input/outputcharacteristic line, and through a maximum luminance point of thereference input/output characteristic line on the basis of the acquiredwhite-side intermediate luminance distribution, and the above-describedcorrection executing means executes image correction on input image datain regions of lower luminance and higher luminance relative to thereference luminance on the basis of the determined low-luminance-regioninput/output characteristic curve and the determinedhigh-luminance-region input/output characteristic curve, respectively.In such a configuration, the high-luminance-region input/outputcharacteristic curve as a part of the above-described input/outputcharacteristic line easily forms a simple curve irrespective of thedescriptions of input image data. Moreover, the above-describedlow-luminance-region input/output characteristic curve is morepreferably a curve provided below the reference input/outputcharacteristic line and not having an inflection point, and theabove-described high-luminance-region input/output characteristic curveis more preferably a curve provided above the reference input/outputcharacteristic line and not having an inflection point. In this case,“an inflection point” means a point at which the sign of the secondderivative of a function defining the curve changes from positive tonegative or from negative to positive. In such a configuration, thelow-luminance-region input/output characteristic curve and thehigh-luminance-region input/output characteristic curve form thesimplest curves, and the effect of improving the contrast is furtherenhanced.

In the image correction circuit, the image correction method and theimage display according to the embodiment of the invention, theintermediate luminance region is determined in each image frame on thebasis of the descriptions of input image data, and the luminancedistribution of input image data in the intermediate luminance region isacquired in each image frame, and on the basis of the acquired luminancedistribution of the intermediate luminance region, the input/outputcharacteristic line is determined in each image frame, and on the basisof the determined input/output characteristic line, image correction oninput image data is executed, so irrespective of the descriptions ofinput image data, the input/output characteristic line can easily form asimple curve. Therefore, for example, even in the case where a luminancehistogram distribution in an image frame includes a large number ofdistribution peaks, an unnatural image is not displayed, and effectivecontrast improvement can be achieved.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit block diagram showing the whole configuration of animage display according to a first embodiment of the invention;

FIG. 2 is a plot for describing a relationship between a luminancedistribution, a weighed luminance center and an intermediate luminanceregion;

FIGS. 3A and 3B are plots for describing a black-side intermediateluminance distribution and a white-side intermediate luminancedistribution;

FIGS. 4A and 4B are plots showing specific examples of an input/outputcharacteristic line according to the first embodiment;

FIGS. 5A and 5B are plots for describing specific examples of arelationship between total distribution volume and gain in anintermediate luminance region;

FIG. 6 is a circuit block diagram showing the configuration ofinput/output characteristic line generating section according to asecond embodiment of the invention;

FIGS. 7A and 7B are plots for describing a black-side luminancedistribution and a white-side luminance distribution;

FIGS. 8A and 8B are plots showing specific examples of an input/outputcharacteristic line according to the second embodiment;

FIGS. 9A and 9B are plots showing other specific examples of theinput/output characteristic line according to the second embodiment;

FIGS. 10A and 10B are plots for describing a relationship between aluminance distribution, a reference luminance, and an intermediateluminance region according to a modification of the invention;

FIGS. 11A and 11B are plots for describing a relationship between aluminance distribution, a reference luminance, and an intermediateluminance region according to a modification of the invention;

FIG. 12 is a plot for describing a relationship between a luminancedistribution, an initial reference luminance, an initial intermediateluminance region and a weighed intermediate luminance center accordingto a modification of the invention;

FIGS. 13A and 13B are plots for describing an example of a relationshipbetween a luminance distribution and the change mode of a gamma curve inan image display in a related art;

FIGS. 14A and 14B are plots for describing another example of arelationship between a luminance distribution and the change mode of agamma curve in an image display in a related art;

FIGS. 15A and 15B are plots for describing still another example of arelationship between a luminance distribution and the change mode of agamma curve in an image display in a related art; and

FIGS. 16A and 16B are plots showing another example of the change modeof a gamma curve in an image display in a related art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments will be described in detail below referring to theaccompanying drawings.

First Embodiment

FIG. 1 shows the whole configuration of an image display according to afirst embodiment of the invention. The image display includes an imageprocessing function section including a tuner 11, a Y/C separationcircuit 12, a chroma decoder 13, a switch 14, a delay circuit 15, aninput/output characteristic line generating section 2 and an imageprocessing section 3, and an image display function section including amatrix circuit 41, a driver 42 and a display 5. An image correctioncircuit and an image correction method according to a first embodimentof the invention are embodied by the image display according to theembodiment, so they will be also described below.

Image signals inputted into the image display may be outputs from a VCR(Video Cassette Recorder), a DVD (Digital Versatile Disc) or the like inaddition to a TV signal from a TV (television). It has become commonpractice for recent televisions and personal computers (PCs) to obtainimage information from a plurality of kinds of media and display animage corresponding to each of the media.

The tuner 11 receives and demodulates the TV signal from the TV, andoutputs the TV signal as a composite video burst signal (CVBS).

The Y/C separation circuit 12 separates the composite video burst signalfrom the tuner 11 or a composite video burst signal from a VCR or a DVD1into a luminance signal Y1 and a chrominance signal C1 to output them.

The chroma decoder 13 outputs the luminance signal Y1 and thechrominance signal C1 separated by the Y/C separation circuit 12 as YUVsignals (Y1, U1, V1) including the luminance signal Y1 andcolor-difference signals U1 and V1.

The YUV signals are image data of a digital image, and a set of pixelvalues corresponding to a position on a two-dimensional image. Aluminance signal Y represents a luminance level, and takes an amplitudevalue between a white level which is 100% white and a black level.Moreover, a 100% white image signal is 100 (IRE) in a unit called IRE(Institute of Radio Engineers) representing a relative ratio of an imagesignal. The black level is 0 IRE. On the other hand, thecolor-difference signals U and V correspond to a signal B-Y produced bysubtracting the luminance signal Y from blue (B), and a signal R-Yproduced by subtracting the luminance signal Y from red (R),respectively, and when the signals U and V are combined with theluminance signal Y, colors (color phases, chroma saturation, luminance)can be shown.

The switch 14 switches YUV signals from a plurality of kinds of media(in this case, the YUV signals (Y1, U1, V1) and YUV signals (Y2, U2, V2)from a DVD2) so as to output selected signals as YUV signals (Yin, Uin,Vin).

The input/output characteristic line generating section 2 adaptivelygenerates an input/output characteristic line (a γ curve) used in the γcorrection execution circuit 31 of the image processing section 3 whichwill be described later, and includes a luminance distributionacquisition circuit 21, a black-side intermediate luminance distributionacquisition circuit 22, a white-side intermediate luminance distributionacquisition circuit 23 and a characteristic line determining section 24.

The luminance distribution acquisition circuit 21 acquires a luminancedistribution as a histogram distribution on the basis of the luminancesignal Yin of the YUV signals (Yin, Uin, Vin) outputted from the switch14, and determines a weighed luminance center of the acquired luminancedistribution to determine an intermediate luminance region centered onthe weighed luminance center. The weighed luminance center is aluminance position corresponding to a value equal to the sum of theproduct of luminance and frequency (total integral) divided by the sumof frequency in a luminance distribution of one image frame.

FIG. 2 shows an example of a luminance distribution (a luminancedistribution 6) acquired by the luminance distribution acquisitioncircuit 21, and the vertical axis indicates frequency of the histogramdistribution, and the horizontal axis indicates luminance level.

The luminance distribution acquisition circuit 21 acquires such aluminance distribution 6 per data for 1 frame when displaying an imageor per data of an image frame (image data constituting one screen) whichis data for 1 field. Moreover, on the basis of such a luminancedistribution 6, the weighed luminance center (for example, a weighedluminance center G1 in FIG. 2) of a luminance distribution is determinedin each image frame, and an area having a predetermined width (in anexample shown in FIG. 2, a width equal to 3 gray levels) from theacquired weighed luminance center G1 to each of a low luminance side anda high luminance side is determined as an intermediate luminance regionin each image frame. In this case, the weighed luminance center G isdetermined by, for example, the following formula 1, and a luminancedistribution can be acquired in each image frame, so the weighedluminance center G can be determined in each image frame. In addition,data of the luminance distribution 6, the weighed luminance center G andthe intermediate luminance region 6M which are acquired in such a manneris outputted to the black-side intermediate luminance distributionacquisition circuit 22 and the white-side intermediate luminancedistribution acquisition circuit 23.

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack & \; \\\begin{matrix}{G = \frac{{{hist}\; 1 \times P_{1}} + {{hist}\; 2 \times P_{2}\mspace{11mu}\cdots} + {{hist}\; m \times P_{m}}}{{{hist}\; 1} + {{hist}\; 2} + \cdots + {{hist}\; m}}} \\{= \frac{\sum\limits_{k = 1}^{m}\left( {{hist}_{k} \times P_{k}} \right)}{\sum\limits_{k = 1}^{m}{hist}_{k}}}\end{matrix} & (1)\end{matrix}$

-   G: weighed luminance center-   m: division number of luminance levels in luminance distribution-   hist_(k): frequency of kth luminance level in luminance distribution-   P_(k): kth luminance level in luminance distribution

On the basis of the data of the luminance distribution 6, the weighedluminance center G and the intermediate luminance region 6M acquired bythe luminance distribution acquisition circuit 21, for example, as shownin FIG. 3A, the black-side intermediate luminance distributionacquisition circuit 22 acquires a black-side intermediate luminancedistribution 61 in each image frame as a luminance distribution in aregion of lower luminance relative to the weighed luminance center G (ablack-side intermediate luminance region 6BM) in the intermediateluminance region 6M determined in each image frame. Likewise, on thebasis of the data of the luminance distribution 6, the weighed luminancecenter G and the intermediate luminance region 6M which are acquired bythe luminance distribution acquisition circuit 21, for example, as shownin FIG. 3B, the white-side intermediate luminance distributionacquisition circuit 23 acquires a white-side intermediate luminancedistribution 62 in each image frame as a luminance distribution in aregion of higher luminance relative to the weighed luminance center G (awhite-side intermediate luminance region 6WM) in the intermediateluminance region 6M determined in each image frame.

Referring back to FIG. 1, for example, as shown in FIG. 4A, on the basisof the black-side intermediate luminance distribution 61 acquired by theblack-side intermediate luminance distribution acquisition circuit 22and the white-side intermediate luminance distribution 62 acquired bythe white-side intermediate luminance distribution acquisition circuit23, the characteristic line determining section 24 determines aninput/output characteristic line (a γ curve) Lout1 which is anadaptively changed reference input/output characteristic line L0representing an input luminance signal Yin=an output luminance signalYout. More specifically, the γ curve Lout1 includes alow-luminance-region input/output characteristic curve LB1, which passesthrough a center point P1 determined by the weighed luminance center G1and the value of the reference input/output characteristic line L0 atthe weighed luminance center G1 and a minimum luminance point P3 of thereference input/output characteristic line L0, and ahigh-luminance-region input/output characteristic curve LW1, whichpasses through the center point P1 and a maximum luminance point P4 ofthe reference input/output characteristic line L0. Thelow-luminance-region input/output characteristic line LB1 and thehigh-luminance-region input/output characteristic line LW1 are providedbelow and above the reference input/output characteristic line L0,respectively, and each of them is represented as a curve not having aninflection point (for example, a quadratic curve), thereby the whole γcurve Lout1 is a S-shaped curve.

As described above, the weighed luminance center is determined in eachimage frame, therefore, for example, as shown in FIG. 4B, it is likelythat the center point, the low-luminance-region input/outputcharacteristic curve, the high-luminance-region input/outputcharacteristic curve and the γ curve are acquired in each image frame,and are different in each image frame (for example, a weighed luminancecenter G2, a center point P2, a low-luminance-region input/outputcharacteristic curve LB2, a high-luminance-region input/outputcharacteristic curve LW2 and a γ curve Lout2 in the drawing).

Moreover, the characteristic line determining section 24 determinesappropriate gain values in the low-luminance-region input/outputcharacteristic curve LB1 and the high-luminance-region input/outputcharacteristic curve LW1, that is, appropriate amounts of adaptivechange from the reference input/output characteristic line L0 on thebasis of the total distribution volume in the black-side intermediateluminance distribution 61 and the total distribution volume in thewhite-side intermediate luminance distribution 62.

In this case, FIG. 5A shows a relationship between the totaldistribution volume in the black-side intermediate luminance region 6BMand a gain (a black-side gain Bg) in the low-luminance-regioninput/output characteristic curve LB1, and FIG. 5B shows a relationshipbetween the total distribution volume in the white-side intermediateluminance region 6WM and a gain (a white-side gain Wg) in thehigh-luminance-region input/output characteristic curve LW1.

In FIGS. 5A and 5B, there are five regions B0 through B4 and fiveregions W0 through W4 separated by black-side distribution thresholdvalues Bt0 through Bt3 and white-side distribution threshold values Wt0through Wt3, respectively, with reference to the value of the totaldistribution volume in the horizontal axis.

More specifically, in FIG. 5A, in the region B0 in which the totaldistribution volume is equal to or less than the black-side distributionthreshold value Bt0, the value of the black-side gain Bg is “0”, and inthe region B1 in which the total distribution volume is larger than theblack-side distribution threshold value Bt0, and is equal to or lessthan the black-side distribution threshold value Bt1, the value of theblack-side gain Bg is increased (in this case, linearly increased) withan increase in the total distribution volume. Moreover, in the region B2in which the total distribution volume is larger than the black-sidedistribution threshold value Bt1, and is equal to or less than theblack-side distribution threshold value Bt2, the black-side gain Bg islimited by the black-side gain threshold value Bg2 so as to be a uniformvalue, and in the regions B3 and B4 in which the total distributionvolume is larger than the black-side distribution threshold value Bt2,the black-side gain Bg is limited to less than the black-side gainthreshold value Bg2. In other words, in the region B3 in which the totaldistribution volume is larger than the black-side distribution thresholdvalue Bt2, and is equal to or less than the black-side distributionthreshold value Bt3, the value of the black-side gain Bg is decreased(in this case, linearly decreased) with an increase in the totaldistribution volume, and in the region B4 in which the totaldistribution volume is larger than the black-side distribution thresholdvalue Bt3, the black-side gain Bg is limited to the black-side gainthreshold value Bg1 which is less than the black-side gain thresholdvalue Bg2 to be a uniform value.

Likewise, in FIG. 5B, in the region W0 in which the total distributionvolume is equal to or less than the white-side distribution thresholdvalue Wt0, the value of the white-side gain Wg is “0”, and in the regionW1 in which the total distribution volume is larger than the white-sidedistribution threshold value Wt0, and is equal to or less than thewhite-side distribution threshold value Wt1, the value of the white-sidegain Wg is increased (in this case, linearly increased) with an increasein the total distribution volume. Moreover, in the region W2 in whichthe total distribution volume is larger than the white-side distributionthreshold value Wt1, and is equal to or less than the white-sidedistribution threshold value Wt2, the white-side gain Wg is limited bythe white-side gain threshold value Wg2 to be a uniform value, and inthe regions W3 and W4 in which the total distribution volume is largerthan the white-side distribution threshold value Wt2, the white-sidegain Wg is limited to less than the white-side gain threshold value Wg2.In other words, in the region W3 in which the total distribution volumeis larger than the white-side distribution threshold value Wt2, and isequal to or less than the white-side distribution threshold value Wt3,the value of the white-side gain Wg is decreased (in this case, linearlydecreased) with an increase in the total distribution volume, and in theregion W4 in which the total distribution volume is larger than thewhite-side distribution threshold value Wt3, the white-side gain Wg islimited to the white-side gain threshold value Wg1 which is less thanthe white-side gain threshold value Wg2 to be a uniform value.

Thus, with reference to the total distribution volumes in the black-sideintermediate luminance region 6BM and the white-side intermediateluminance region 6WM, the black-side gain Bg and the white-side gain Wgare increased to the black-side distribution threshold value Bt1 and thewhite-side distribution threshold value Wt1, respectively, according tothe total distribution volumes and in the case where the totaldistribution volumes are larger than the black-side distributionthreshold value Bt1 and the white-side distribution threshold value Wt1,the values of the black-side gain Bg and the white-side gain Wg arelimited, so a gain in the intermediate luminance region 6M is adjustedso as not to be excessive, as will be described in detail later.

Referring back to FIG. 1, the delay circuit 15 delays thecolor-difference signals Uin and Vin outputted from the switch 14, andsynchronizes the color-difference signals Uin and Vin and the γ curveLout outputted from the input/output characteristic line generatingsection 2 to output them to the image processing section 3.

The image processing section 3 performs predetermined image processingon the YUV signals (Yin, Uin, Vin) which are outputted from the switch14 and pass through the delay circuit 15 through the use of the γ curveLout which is adaptively generated by the input/output characteristicline generating section 2, and in the image display according to theembodiment, the image processing section 3 includes the γ correctionexecution circuit 31 performing a contrast improvement process on theYUV signals (Yin, Uin, Vin).

The γ correction execution circuit 31 performs a contrast improvementprocess on the YUV signals (Yin, Uin, Vin) through the use of the γcurve Lout adaptively generated by the input/output characteristic linegenerating section 2. More specifically, for example, as shown in FIGS.4A and 4B, the contrast of the input luminance signal Yin is controlledto a degree shown in a gain in each luminance level by γ curves Lout1and Lout2 determined in each image frame. The YUV signals (Yout, Uout,Vout) after image processing (controlling the contrast) are outputted tothe matrix circuit 41.

The matrix circuit 41 reproduces RGB signals from the YUV signals (Yout,Uout, Vout) after image processing by the image processing section 3,and outputs the reproduced RGB signals (Rout, Gout, Bout) to the driver42.

The driver 42 produces a driving signal for the display 5 on the basisof the RGB signals (Rout, Gout, Bout) outputted from the matrix circuit41, and outputs the driving signal to the display 5.

The display 5 displays an image on the basis of the YUV signals (Yout,Uout, Vout) after image processing by the image processing section 3according to the driving signal outputted from the driver 42. Thedisplay 5 may be any kind of display device. For example, a CRT(Cathode-Ray Tube) 51, a LCD (Liquid Crystal Display) 52, a PDP (PlasmaDisplay Panel; not shown) or the like is used.

In this case, the input/output characteristic line generating section 2and the image processing section 3 correspond to specific examples of“an image correction circuit” in the invention, and the luminancedistribution acquisition circuit 21, the black-side intermediateluminance distribution acquisition circuit 22 and the white-sideintermediate luminance distribution acquisition circuit 23 correspond tospecific examples of “a luminance distribution acquiring means” in theinvention. Moreover, the characteristic line determining section 24corresponds to a specific example of “a determining means” in theinvention, and the γ correction execution circuit 31 corresponds to aspecific example of “a correction executing means” in the invention.

Next, referring to FIGS. 1 through 5A and 5B, the operation of the imagedisplay according to the embodiment will be described below.

At first, an image signal to be inputted into the image display isdemodulated into the YUV signals. More specifically, a TV signal fromthe TV is demodulated into a composite video burst signal by the tuner11, and a composite video burst signal is directly inputted into theimage display from the VCR or the DVD1. Then, the composite video burstsignals are separated into the luminance signal Y1 and the chrominancesignal C1 in the Y/C separation circuit 12, and then the luminancesignal Y1 and the chrominance signal C1 are decoded into the YUV signals(Y1, U1, V1) in the chroma decoder 13. On the other hand, YUV signals(Y2, U2, V2) are directly inputted into the image display from the DVD2.

Next, in the switch 14, either the YUV signals (Y1, U1, V1) or the YUVsignals (Y2, U2, V2) are selected to be outputted as the YUV signals(Yin, Uin, Vin). Then, the luminance signal Yin of the YUV signals (Yin,Uin, Vin) is outputted into the input/output characteristic linegenerating section 2 and the γ correction execution circuit 31 in theimage processing section 3, and the color-difference signals Uin and Vinare outputted to the delay circuit 15.

In the input/output characteristic line generating section 2, thefollowing operation of generating the γ curve Lout is performed on thebasis of the inputted luminance signal Yin.

More specifically, at first, in the luminance distribution acquisitioncircuit 21, for example, a luminance distribution as a histogramdistribution as shown in FIG. 2 is acquired in each image frame on thebasis of the luminance signal Yin of the YUV signals (Yin, Uin, Vin)outputted from the switch 14. Moreover, on the basis of the acquiredluminance distribution, the weighed luminance center G1 is determined ineach image frame, and a predetermined width from the weighed luminancecenter G1 to each of a low luminance side and a high luminance side isset so that the intermediate luminance region is determined in eachimage frame.

Next, in the black-side intermediate luminance distribution acquisitioncircuit 22 and the white-side intermediate luminance distributionacquisition circuit 23, on the basis of the data of the luminancedistribution 6, the weighed luminance center G and the intermediateluminance region 6M acquired by the luminance distribution acquisitioncircuit 21, the black-side intermediate luminance distribution 61 andthe white-side intermediate luminance distribution 62 are acquired ineach image frame.

Then, in the characteristic line determining section 24, on the basis ofthe black-side intermediate luminance distribution 61 acquired by theblack-side intermediate luminance distribution acquisition circuit 22and the white-side intermediate luminance distribution 62 acquired bythe white-side intermediate luminance distribution acquisition circuit23, the reference input/output characteristic line L0 is adaptivelychanged, and the input/output characteristic line (γ curve) Lout1including the low-luminance-region input/output characteristic curve LB1and the high-luminance-region input/output characteristic curve LW1 isdetermined. Moreover, for example, as shown in FIGS. 5A, and 5B,appropriate values of gains (the black-side gain Bg and the white-sidegain Wg) in the low-luminance-region input/output characteristic curveLB1 and the high-luminance-region input/output characteristic curve LW1,that is, appropriate amounts of adaptive change from the referenceinput/output characteristic line L0 are determined on the basis of thetotal distribution volume in the black-side intermediate luminancedistribution 61 and the total distribution volume in the white-sideintermediate luminance distribution 62. More specifically, withreference to the total distribution volumes in the black-sideintermediate luminance region 6BM and the white-side intermediateluminance region 6WM, the black-side gain Bg and the white-side gain Wgare increased to the black-side distribution threshold value Bt1 and thewhite-side distribution threshold value Wt1, respectively, according tothe total distribution volumes, and in the case where the totaldistribution volumes are larger than the black-side distributionthreshold value Bt1 and the white-side distribution threshold value Wt1,the values of the black-side gain Bg and the white-side gain Wg arelimited so as to prevent a gain in the intermediate luminance region 6Mfrom being excessive. The γ curve Lout adaptively generated in eachimage frame in such a manner is outputted to the γ correction executioncircuit 31 in the image processing section 3.

On the other hand, the delay circuit 15 delays the color-differencesignals Uin and Vin, and as a result, the color-difference signals Uinand Vin and the γ curve Lout outputted from the input/outputcharacteristic line generating section 2 are synchronized.

Next, in the γ correction execution circuit 31 of the image processingsection 3, on the basis of the luminance signal Yin outputted from theswitch 14 and the color-difference signals Uin and Vin outputted fromthe switch 14 and passing through the delay circuit 15, a contrastimprovement process is performed on the YUV signals (Yin, Yin and Vin)through the use of the γ curve Lout supplied from the input/outputcharacteristic line generating section 2. More specifically, thecontrast is controlled to degrees shown in the black-side gain Bg in thelow-luminance-region input/output characteristic curve LB1 and thewhite-side gain Wg in the high-luminance-region input/outputcharacteristic curve LW1 in each luminance level.

The γ curve Lout includes the low-luminance-region input/outputcharacteristic curve LB1 and the high-luminance-region input/outputcharacteristic curve LW1 which are input/output characteristic lines inwider regions (regions of lower luminance and higher luminance relativeto the weighed luminance center G1) than the black-side intermediateluminance distribution 61 and the white-side intermediate luminancedistribution 62 on the basis of the black-side intermediate luminancedistribution 61 and the white-side intermediate luminance distribution62 which are luminance distributions in local regions, so thelow-luminance-region input/output characteristic curve LB1 and thehigh-luminance-region input/output characteristic curve LW1, and byextension to the γ curve Lout easily form simple curves irrespective ofthe descriptions of an input image (the YUV signals (Yin, Uin, Vin)).More specifically, in the embodiment, the low-luminance-regioninput/output characteristic curve LB1 and the high-luminance-regioninput/output characteristic curve LW1 each include a quadratic curve nothaving an inflection point, so irrespective of the descriptions of theinput image, that is, the histogram distribution of the input luminancesignal Yin in each image frame, the γ curve Lout is a simple S-shapedcurve.

Therefore, for example, in the case of an input image in which a largenumber of peaks exist in the luminance distribution, in an image displayin a related art, as in the case of the gamma curves L105A and L105Bshown in FIGS. 14A and 14B, the gamma curve is complicated, so theeffect of improving the contrast is reduced (refer to FIG. 14A), or thegamma curve has a negative slope, thereby a displayed image appearsunnatural (refer to FIG. 14B). On the other hand, in the image displayaccording to the embodiment, the γ curve Lout easily forms a simpleS-shaped curve, so compared to the related art, the contrast of thedisplayed image is more effectively improved, and the displayed image isprevented from appearing unnatural.

Moreover, as shown in FIGS. 5A and 5B, with respect to the totaldistribution volumes in the black-side intermediate luminance region 6BMand the white-side intermediate luminance region 6WM, the black-sidegain Bg and the white-side gain Wg are increased to the black-sidedistribution threshold value Bt1 and the white-side distributionthreshold value Wt1, respectively, according to the total distributionvolumes, so a gain is appropriately set so as to increase the contrastaccording to the total distribution volumes. Moreover, in the case wherethe total distribution volume is larger than the black-side distributionthreshold value Bt1 or the white-side distribution threshold value Wt1,the values of the black-side gain Bg and the white-side gain Wg arelimited so as to prevent a gain in the intermediate luminance region 6Mfrom being excessive. Therefore, for example, even in an enlarged imageof a person's skin, the skin contour is not emphasized too much, and amore natural image is displayed. Moreover, in the case where the totaldistribution volume is larger than the black-side distribution thresholdvalue Bt2 or the white-side distribution threshold value Wt2, the valuesof the black-side gain Bg and the white-side gain Wg are further limited(to less than the black-side gain threshold value Bg2 and the white-sidegain threshold value Wg2, respectively), so even if the totaldistribution volumes are further increased, a gain in the intermediateluminance region 6M is reliably limited so as not to be excessive.

Next, the matrix circuit 41 reproduces RGB signals (Rout, Gout, Bout)from the YUV signals (Yout, Uout, Vout) after contrast processing, andthe driver 42 produces a driving signal on the basis of the RGB signals(Rout, Gout, Bout), and an image is displayed on the display 5 on thebasis of the driving signal.

As described above, in the embodiment, in the luminance distributionacquisition circuit 21, the intermediate luminance region 6M isdetermined in each image frame on the basis of the input luminancesignal Yin, and in the black-side intermediate luminance distributionacquisition circuit 22 and the white-side intermediate luminancedistribution acquisition circuit 23, the luminance distributions (theblack-side intermediate luminance distribution 61 and the white-sideintermediate luminance distribution 62) in the intermediate luminanceregion 6M are acquired in each image frame, and in the characteristicline determining section 24, on the basis of the black-side intermediateluminance distribution 61 and the white-side intermediate luminancedistribution 62, a reference input/output characteristic line L0 isadaptively changed, so the γ curve Lout is determined in each imageframe, and in the γ correction execution circuit 31, on the basis of theγ curve Lout, image correction on the YUV signals (Yin, Uin, Vin) isexecuted, so irrespective of the descriptions of input image data, the γcurve Lout can easily form a simple curve. Therefore, for example, evenin the case where the luminance histogram distribution in the imageframe includes a large number of distribution peaks, the displayed imagedoes not appear unnatural, and effective contrast improvement can beachieved.

More specifically, the black-side intermediate luminance distribution 61and the white-side intermediate luminance distribution 62 in theintermediate luminance region 6M in the luminance distribution 6 of theluminance signal Yin in each image frame are acquired in each imageframe, and in the characteristic line determining section 24, on thebasis of the black-side intermediate luminance distribution 61 and thewhite-side intermediate luminance distribution 62, thelow-luminance-region input/output characteristic curve LB1 passingthrough the reference point (the weighed luminance center G1) and theminimum luminance point P3 and the high-luminance-region input/outputcharacteristic curve LW1 passing through the weighed luminance center G1and the maximum luminance point P4 are determined in each image frame,and in the γ correction execution circuit 31, on the basis of thedetermined low-luminance-region input/output characteristic curve LB1and the determined high-luminance-region input/output characteristiccurve LW1, image correction on the YUV signals (Yin, Uin, Vin) inregions of lower luminance and higher luminance relative to the weighedluminance center G1 is performed, so irrespective of the descriptions ofinput image date, the low-luminance-region input/output characteristiccurve LB1 and the high-luminance-region input/output characteristiccurve LW1 each can easily form a simple curve.

Moreover, in the case where the total distribution volume of theblack-side intermediate luminance region 6BM or the white-sideintermediate luminance region 6WM is larger than the black-sidedistribution threshold value Bt1 or the white-side distributionthreshold value Wt1, the values of the black-side gain Bg and thewhite-side gain Wg are limited, so a gain in the intermediate luminanceregion 6M can be prevented from being excessive. Therefore, for example,in an enlarged image of a person's skin, the skin contour is notemphasized too much, and a more natural image can be displayed.

Moreover, in the case where the total distribution volume in theblack-side intermediate luminance region 6BM or the white-sideintermediate luminance region 6WM is larger than the black-sidedistribution threshold value Bt2 or the white-side distributionthreshold value Wt2, the values of the black-side gain Bg and thewhite-side gain Wg are further limited (to less than the black-side gainthreshold value Bg2 and the white-side gain threshold value Wg2,respectively), so even if the total distribution volume is furtherincreased, a gain in the intermediate luminance region 6M can bereliably prevented from being excessive.

Further, the black-side intermediate luminance distribution acquisitioncircuit 22 and the white-side intermediate luminance distributionacquisition circuit 23 are separately arranged, so the operation ofimproving the contrast in the low luminance region and the operation ofimproving the contrast in the high luminance region can be separatelyperformed.

Second Embodiment

Next, a second embodiment of the invention will be described below. Animage display according to the embodiment further includes a black-sideluminance distribution acquisition circuit 25 and a white-side luminancedistribution acquisition circuit 26 in the input-output characteristicline generating section 2 in the image display according to the firstembodiment.

FIG. 6 shows the configuration of an input/output characteristic linegenerating section 2A according to the embodiment. The input/outputcharacteristic line generating section 2A according to the embodimentincludes the luminance distribution acquisition circuit 21, theblack-side intermediate luminance distribution acquisition circuit 22,the white-side intermediate luminance distribution acquisition circuit23, the characteristic line determining section 24, the black-sideluminance distribution acquisition circuit 25 and the white-sideluminance distribution acquisition circuit 26. Like components aredenoted by like numerals as of the first embodiment and will not befurther described.

For example, as shown in FIG. 7A, the black-side luminance distributionacquisition circuit 25 acquires a black-side luminance distribution 63in each image frame as a luminance distribution in a region (ablack-side luminance region 6B) on a lower luminance side than theintermediate luminance region 6M determined in each image frame on thebasis of data of the luminance distribution 6, the weighed luminancecenter G and the intermediate luminance region 6M acquired by theluminance distribution acquisition circuit 21. Likewise, for example, asshown in FIG. 7B, the white-side luminance distribution acquisitioncircuit 26 acquires a white-side luminance distribution 64 in each imageframe as a luminance distribution in a region (a white-side luminanceregion 6W) on a higher luminance side than the intermediate luminanceregion 6M determined in each image frame on the basis of the data of theluminance distribution 6, the weighed luminance center G and theintermediate luminance region 6M acquired by the luminance distributionacquisition circuit 21.

In this case, the luminance distribution acquisition circuit 21, theblack-side intermediate luminance distribution acquisition circuit 22,the white-side intermediate luminance distribution acquisition circuit23, the black-side luminance distribution acquisition circuit 25 and thewhite-side luminance distribution acquisition circuit 26 correspond tospecific examples of “a luminance distribution acquiring means” in theinvention.

In the input/output characteristic line generating section 2A accordingto the embodiment, the following operation of generating the γ curveLout is performed on the basis of the inputted luminance signal Yin.

At first, in the luminance distribution acquisition circuit 21, as inthe case of the first embodiment, the luminance distribution 6 as ahistogram distribution is acquired in each image frame on the basis ofthe luminance signal Yin, and on the basis of the acquired luminancedistribution, the weighed luminance center G1 and the intermediateluminance region 6M are determined in each image frame. Next, in theblack-side intermediate luminance distribution acquisition circuit 22and the white-side intermediate luminance distribution acquisitioncircuit 23, as in the case of the first embodiment, on the basis of thedata of the luminance distribution 6, the weighed luminance center G andthe intermediate luminance region 6M, the black-side intermediateluminance distribution 61 and the white-side intermediate luminancedistribution 62 are acquired in each image frame. On the other hand, inthe black-side luminance distribution acquisition circuit 25 and thewhite-side luminance distribution acquisition circuit 26, on the basisof the data of the luminance distribution 6, the weighed luminancecenter G and the intermediate luminance region 6M, the black-sideluminance distribution 63 and the white-side luminance distribution 64are acquired in each image frame.

Next, in the characteristic line determining section 24, as in the caseof the first embodiment, on the basis of the black-side intermediateluminance distribution 61 acquired by the black-side intermediateluminance distribution acquisition circuit 22 and the white-sideintermediate luminance distribution 62 acquired by the white-sideintermediate luminance distribution acquisition circuit 23, thelow-luminance-region input/output characteristic curve LB1 and thehigh-luminance-region input/output characteristic curve LW1 aregenerated.

In the characteristic line determining section 24 according to theembodiment, when the γ curve Lout is finally determined, the γ curveLout is determined on the basis of the black-side luminance distribution63 acquired by the black-side luminance distribution acquisition circuit25 and the white-side luminance distribution 64 acquired by thewhite-side luminance distribution acquisition circuit 26 in addition tothe low-luminance-region input/output characteristic curve LB1 and thehigh-luminance-region input/output characteristic curve LW1. Morespecifically, as in the case of a γ curve Lout11 shown in FIG. 8A, thegain of an input/output characteristic line L10B generated on the basisof the black-side luminance distribution 63 and the gain of aninput/output characteristic line L10W generated on the basis of thewhite-side luminance distribution 64 are superimposed on the gains ofthe low-luminance-region input/output characteristic curve LB1 and thehigh-luminance-region input/output characteristic curve LW1 so as tofinally determine the γ curve Lout11 including a low-luminance-regioninput/output characteristic curve LB11 and a high-luminance-regioninput/output characteristic curve LW11. Therefore, the γ curve Lout11 isdetermined in consideration of the luminance distributions in theblack-side luminance region 6B and the white-side luminance region 6W inaddition to the luminance distribution in the intermediate luminanceregion 6M so as to adjust the γ curve more finely.

Moreover, for example, as shown in FIG. 8B, in the case where as aresult of superimposing the gains of the input/output characteristicline L10B and the input/output characteristic line L10W on the gains ofthe low-luminance-region input/output characteristic curve LB1 and thehigh-luminance-region input/output characteristic curve LW1, the gain ofthe low-luminance-region input/output characteristic curve LB11 or thehigh-luminance-region input/output characteristic curve LW11 becomesexcessive, and in a part of the black-side luminance region 6B or thewhite-side luminance region 6W, even though an input is changed, anoutput is not changed, so it is difficult to show gray levels, the gainsof the input/output characteristic line L10B and the input/outputcharacteristic line L10W are corrected so as to be smaller, and the gainof the low-luminance-region input/output characteristic curve LB11 orthe high-luminance-region input/output characteristic curve LW11 isprevented from being excessive. Therefore, a part of the black-sideluminance region 6B or the white-side luminance region 6W can beprevented from being collapsed, and gray levels can be displayedreliably.

In addition, for example, as shown in FIG. 9A, in the case where aninput/output characteristic line generated on the basis of theblack-side luminance distribution 63 or the white-side luminancedistribution 64 has a shape like an input/output characteristic line L20in the drawing, the input/output characteristic line is determined likea γ curve Lout21 in the drawing in a like manner, and in the case wherethe gain at this time becomes excessive, like an input/outputcharacteristic line L21 shown in FIG. 9B, the gain of the γ curve Lout21is corrected so as not to become excessive.

As described above, in the embodiment, when the γ curve Lout is finallydetermined, the γ curve Lout is determined in consideration of theblack-side luminance distribution 63 acquired by the black-sideluminance distribution acquisition circuit 25 and the white-sideluminance distribution 64 acquired by the white-side luminancedistribution acquisition circuit 26 in addition to thelow-luminance-region input/output characteristic curve LB1 and thehigh-luminance-region input/output characteristic curve LW1, so when theγ curve Lout11 is determined also in consideration of the luminancedistributions in the black-side luminance region 6B and the white-sideluminance region 6W, the γ curve can be adjusted more finely.

More specifically, for example, in the case where as a result ofsuperimposing the gains of the input/output characteristic line L10B andthe input/output characteristic line L10W, the gain of thelow-luminance-region input/output characteristic curve LB11 or thehigh-luminance-region input/output characteristic curve LW11 becomesexcessive, and it is difficult to display gray levels in a part of theblack-side luminance region 6B or the white-side luminance region 6W,the gains of the input/output characteristic line L10B and theinput/output characteristic line L10W are corrected so as to be smaller,so a part of the black-side luminance region 6B or the white-sideluminance region 6W can be prevented from being collapsed, and graylevels can be displayed reliably.

Moreover, the black-side luminance distribution acquisition circuit 25and the white-side luminance distribution acquisition circuit 26 areseparately arranged, so in the embodiment, the operation of improvingthe contrast in the low luminance region and the operation of improvingthe contrast in the high luminance region can be separately performed.

Although the present invention is described referring to the firstembodiment and the second embodiment, the invention is not limited tothem, and can be variously modified.

For example, in the above-described embodiment, in the case where theweighed luminance center G1 is determined on the basis of the luminancedistribution 6 in the whole luminance region as shown in FIG. 2, and theintermediate luminance region is determined on the basis of the weighedluminance center G1, an area having a predetermined width (in theexample shown in FIG. 2, a width equal to 3 gray levels) from theweighed intermediate luminance center to each of a low luminance side asa black side and a high luminance side as a white side is determined asthe as the intermediate luminance region 6M in each image frame.However, in the case where the weighed luminance center G1 is biased toa black side as shown in FIG. 10A (in the case where a weighed luminancecenter G1 l is provided on a lower luminance side than a weighedluminance center G1 c), an input/output characteristic line Lout3including a low-luminance-region input/output characteristic curve LB3both passing through a center point P30 and a high-luminance-regioninput/output characteristic curve LW3 is determined by thecharacteristic line determining section 24; however, by thelow-luminance-region input/output characteristic curve LB3, as shown inthe drawing, a black gain is excessively reduced, so it is difficult toreproduce details of black, thereby an image appears too dark. Moreover,in the case where the weighed luminance center G1 is biased to a whiteside as shown in FIG. 11A (in the case where a weighed luminance centerG1 h is provided on a higher luminance side than the weighed lumimancecenter G1 c), an input/output characteristic line Lout5 including alow-luminance-region input/output characteristic curve LB5 both passingthrough a center point P50 and a high-luminance-region input/outputcharacteristic curve LW5 is determined by the characteristic linedetermining section 24; however, by the high-luminance-regioninput/output characteristic curve LB5, as shown in the drawing, a whitegain is excessively increased, so as a result, an image appears toobright.

Thus, in the case where the weighed luminance center G1 is biased to ablack side or a white side, as shown in FIG. 10B or FIG. 11B, an area inwhich the width is the same as that of the intermediate luminance region6M, and a width from the weighed intermediate luminance center on a sidewhere the weighed luminance center G1 is biased is narrower and a widthon the other side is wider is determined as an intermediate region 6Mv,so the black gain or the white gain can be prevented from becomingexcessive, thereby more effective contract improvement can be achieved.

For example, in the above-described embodiments, the case where theweighed luminance center G1 is determined on the basis of the luminancedistribution 6 in the whole luminance region as shown in FIG. 2, and theintermediate luminance region 6M is determined on the basis of theweighed luminance center G1 is described; however, for example, as shownin FIG. 12, a weighed luminance center (a weighed intermediate luminancecenter G1M) is determined on the basis of a luminance distribution in apredetermined initial intermediate luminance region 6M0, and an areahaving a predetermined width (in the example shown in FIG. 12, a widthequal to 3 gray levels) from the weighed intermediate luminance centerG1M to each of a low luminance side and a high luminance side may bedetermined as an intermediate luminance region 6M in each image frame.In such a configuration, the same effects as those in theabove-described embodiments can be obtained.

Moreover, in the above-described embodiments, the relationship betweenthe total distribution volume in the black-side intermediate luminanceregion 6BM or the white-side intermediate luminance region 6WM and theblack-side gain Bg or the white-side gain Wg is described in detailreferring to FIGS. 5A and 5B; however, the invention is not limited tothis case. For example, in the regions B2 and W2 and the region B4 andW4, the black-side gain Bg and the white-side gain Wg may not have auniform value, and may be slightly increased or decreased to a degree towhich the gains do not become excessive. Further, the black-side gain Bgand the white-side gain Wg may be increased from the regions B0 and W0,or gains may be decreased directly from the region B2 and W2 to theregions B4 and W4 without arranging the regions B3 and W3.

In the above-described embodiments, the case where the black-sideintermediate luminance distribution acquisition circuit 22 and thewhite-side intermediate luminance distribution acquisition circuit 23are arranged in the input/output characteristic line generating section2, or in addition to them, the black-side luminance distributionacquisition circuit 25 and the white-side luminance distributionacquisition circuit 26 are arranged in the input/output characteristicline generating section 2A so as to concurrently perform the contrastimprovement process on a low luminance side and the contrast improvementprocess on a high luminance side is described; however, only either ofthe black-side intermediate luminance distribution acquisition circuit22 and the white-side intermediate luminance distribution acquisitioncircuit 23 may be arranged, or in addition to this, only either of theblack-side luminance distribution acquisition circuit 25 and thewhite-side luminance distribution acquisition circuit 26 may be arrangedso as to perform the contrast improvement process on either of the lowluminance side and the high luminance side. Even in such aconfiguration, a more natural image than that in a related art can bedisplayed, and the contrast can be effectively improved.

In the above-described embodiments, the case where the image processingsection 3 includes the γ correction execution circuit 31 is described;however, the configuration of the image processing section 3 is notlimited to this case, and the image processing section 3 may include,for example, another circuit for image processing, or a plurality ofsuch circuits.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. An image correction circuit comprising: a region determining meansfor determining an intermediate luminance region in each image frame onthe basis of descriptions of input image data by calculating a weighedluminance center of a luminance distribution of the input image data ineach entire image frame, the weighed luminance center being a luminanceposition corresponding to a sum of a product of luminance and frequencydivided by a sum of frequency in the luminance distribution, theintermediate luminance region including a black-intermediate region anda white-intermediate region, a size of the black-intermediate regionbeing different from a size of the white-intermediate region in responseto whether the weighted luminance center is biased to a low luminanceside or a high luminance side, and a black-side luminance region and awhite-side luminance region based on the luminance distribution, theweighted luminance center, and the intermediate luminance region, theblack-side luminance region being a region of luminance that is lowerthan the lowest luminance in the intermediate luminance region, thewhite-side luminance region being a region of luminance that is higherthan the highest luminance in the intermediate luminance region, and theintermediate luminance region, the black-side luminance region, and thewhite-side luminance region being different and non-overlapping; aluminance distribution acquiring means for acquiring the luminancedistribution of the input image data in the determined intermediateluminance region in each image frame; a determining means fordetermining an input/output characteristic line in each image frame byadaptively changing a predetermined reference input/outputcharacteristic line on the basis of the acquired luminance distributionof the intermediate luminance region, the input/output characteristicline defining the substance of image correction on the input image data;and a correction executing means for executing image correction on theinput image data on the basis of the determined input/outputcharacteristic line.
 2. The image correction circuit according to claim1, wherein the region determining means determines an area as theintermediate luminance region, the area determined by setting a firstwidth from the acquired weighed luminance center to the low luminanceside by setting a second width from the weighed luminance center to thehigh luminance side.
 3. The image correction circuit according to claim1, wherein the luminance distribution acquiring means acquires ablack-side intermediate luminance distribution in each image frame as aluminance distribution in a region between a lowest luminance in thedetermined intermediate luminance region and a reference luminanceprovided in the center of the intermediate luminance region, thedetermining means determines a low-luminance-region input/outputcharacteristic curve on the basis of the acquired black-sideintermediate luminance distribution, the low-luminance-regioninput/output characteristic curve passing through a reference point, inthe reference input/output characteristic line, determined in accordancewith the reference luminance and through a minimum luminance point ofthe reference input/output characteristic line, and the correctionexecuting means executes image correction on input image data having aluminance side which is lower than the reference luminance on the basisof the determined low-luminance-region input/output characteristiccurve.
 4. The image correction circuit according to claim 3, wherein thelow-luminance-region input/output characteristic curve is a curveprovided below the reference input/output characteristic line and nothaving an inflection point.
 5. The image correction circuit according toclaim 3, wherein the luminance distribution acquiring means furtheracquires a black-side luminance distribution as a luminance distributionin the black-side luminance region, and the determining means determinesthe low-luminance-region input/output characteristic curve on the basisof the acquired black-side luminance distribution as well as theblack-side intermediate luminance distribution.
 6. The image correctioncircuit according to claim 3, wherein the luminance distributionacquiring means further acquires a white-side intermediate luminancedistribution as a luminance distribution in a region between a highestluminance in the determined intermediate luminance region and thereference luminance, the determining means further determines ahigh-luminance-region input/output characteristic curve passing throughthe reference point in the reference input/output characteristic line,and through a maximum luminance point of the reference input/outputcharacteristic line on the basis of the acquired white-side intermediateluminance distribution, and the correction executing means executesimage correction on input image data in regions of lower luminance andhigher luminance relative to the reference luminance on the basis of thedetermined low-luminance-region input/output characteristic curve andthe determined high-luminance-region input/output characteristic curve,respectively.
 7. The image correction circuit according to claim 6,wherein the high-luminance-region input/output characteristic curve is acurve provided above the reference input/output characteristic line andnot having an inflection point.
 8. The image correction circuitaccording to claim 6, wherein the luminance distribution acquiring meansfurther acquires a white-side luminance distribution as a luminancedistribution in the white-side luminance region, and the determiningmeans determines the high-luminance-region input/output characteristiccurve on the basis of the acquired white-side luminance distribution aswell as the white-side intermediate luminance distribution.
 9. The imagecorrection circuit according to claim 1, wherein the luminancedistribution acquiring means acquires a white-side intermediateluminance distribution in each image frame as a luminance distributionin a region between a highest luminance in the determined intermediateluminance region and a reference luminance provided in the center of theintermediate luminance region, the determining means determines ahigh-luminance-region input/output characteristic curve on the basis ofthe acquired white-side intermediate luminance distribution, thehigh-luminance-region input/output characteristic line passing through areference point, in the reference input/output characteristic line,determined in accordance with the reference luminance and through amaximum luminance point of the reference input/output characteristicline, and the correction executing means executes image correction oninput image data having a luminance which is higher than the referenceluminance on the basis of the determined high-luminance-regioninput/output characteristic curve.
 10. An image correction method beingperformed using an image correction device having a processor, themethod comprising the steps of: determining an intermediate luminanceregion in each image frame on the basis of descriptions of input imagedata by calculating a weighed luminance center of a luminancedistribution of the input image data in each entire image frame, theweighed luminance center being a luminance position corresponding to asum of a product of luminance and frequency divided by a sum offrequency in the luminance distribution the intermediate luminanceregion including a black-intermediate region and a white-intermediateregion, a size of the black-intermediate region being different from asize of the white-intermediate region in response to whether theweighted luminance center is biased to a low luminance side or a highluminance side; determining a black-side luminance region and awhite-side luminance region based on the luminance distribution, theweighted luminance center, and the intermediate luminance region, theblack-side luminance region being a region of luminance that is lowerthan the lowest luminance in the intermediate luminance region, thewhite-side luminance region being a region of luminance that is higherthan the highest luminance in the intermediate luminance region, and theintermediate luminance region, the black-side luminance region, and thewhite-side luminance region being different and non-overlapping;acquiring the luminance distribution of the input image data in thedetermined intermediate luminance region in each image frame;determining, using the processor, an input/output characteristic line ineach image frame by adaptively changing a predetermined referenceinput/output characteristic line on the basis of the acquired luminancedistribution of the intermediate luminance region, the input/outputcharacteristic line defining the substance of image correction on theinput image data; and executing image correction on the input image dataon the basis of the determined input/output characteristic line.
 11. Animage display comprising: a region determining means for determining anintermediate luminance region in each image frame on the basis ofdescriptions of input image data by calculating a weighed luminancecenter of a luminance distribution of the input image data in eachentire image frame, the weighed luminance center being a luminanceposition corresponding to a sum of a product of luminance and frequencydivided by a sum of frequency in the luminance distribution, theintermediate luminance region including a black-intermediate region anda white-intermediate region, a size of the black-intermediate regionbeing different from a size of the white-intermediate region in responseto whether the weighted luminance center is biased to a low luminanceside or a high luminance side, and a black-side luminance region and awhite-side luminance region based on the luminance distribution, theweighted luminance center, and the intermediate luminance region, theblack-side luminance region being a region of luminance that is lowerthan the lowest luminance in the intermediate luminance region, thewhite-side luminance region being a region of luminance that is higherthan the highest luminance in the intermediate luminance region, and theintermediate luminance region, the black-side luminance region, and thewhite-side luminance region being different and non-overlapping; aluminance distribution acquiring means for acquiring the luminancedistribution of the input image data in the determined intermediateluminance region in each image frame; a determining means fordetermining an input/output characteristic line in each image frame byadaptively changing a predetermined reference input/outputcharacteristic line on the basis of the acquired luminance distributionof the intermediate luminance region, the input/output characteristicline defining the substance of image correction on input image data; acorrection executing means for executing image correction on the inputimage data on the basis of the determined input/output characteristicline, and a display means for displaying an image on the basis of theinput image data on which image correction is performed.
 12. An imagecorrection circuit comprising: a region determining section determiningan intermediate luminance region in each image frame on the basis ofdescriptions of input image data by calculating a weighed luminancecenter of a luminance distribution of the input image data in eachentire image frame, the weighed luminance center being a luminanceposition corresponding to a sum of a product of luminance and frequencydivided by a sum of frequency in the luminance distribution, theintermediate luminance region including a black-intermediate region anda white-intermediate region, a size of the black-intermediate regionbeing different from a size of the white-intermediate region in responseto whether the weighted luminance center is biased to a low luminanceside or a high luminance side, and a black-side luminance region and awhite-side luminance region based on the luminance distribution, theweighted luminance center, and the intermediate luminance region, theblack-side luminance region being a region of luminance that is lowerthan the lowest luminance in the intermediate luminance region, thewhite-side luminance region being a region of luminance that is higherthan the highest luminance in the intermediate luminance region, and theintermediate luminance region, the black-side luminance region, and thewhite-side luminance region being different and non-overlapping; aluminance distribution acquiring section acquiring the luminancedistribution of the input image data in the determined intermediateluminance region in each image frame; a determining section determiningan input/output characteristic line in each image frame by adaptivelychanging a predetermined reference input/output characteristic line onthe basis of the acquired luminance distribution of the intermediateluminance region, the input/output characteristic line defining thesubstance of image correction on the input image data; and a correctionexecuting section executing image correction on the input image data onthe basis of the determined input/output characteristic line.
 13. Animage display comprising: a region determining section determining anintermediate luminance region in each image frame on the basis ofdescriptions of input image data by calculating a weighed luminancecenter of a luminance distribution of the input image data in eachentire image frame, the weighed luminance center being a luminanceposition corresponding to a sum of a product of luminance and frequencydivided by a sum of frequency in the luminance distribution, theintermediate luminance region including a black-intermediate region anda white-intermediate region, a size of the black-intermediate regionbeing different from a size of the white-intermediate region in responseto whether the weighted luminance center is biased to a low luminanceside or a high luminance side, and a black-side luminance region and awhite-side luminance region based on the luminance distribution, theweighted luminance center, and the intermediate luminance region, theblack-side luminance region being a region of luminance that is lowerthan the lowest luminance in the intermediate luminance region, thewhite-side luminance region being a region of luminance that is higherthan the highest luminance in the intermediate luminance region, and theintermediate luminance region, the black-side luminance region, and thewhite-side luminance region being different and non-overlapping; aluminance distribution acquiring section acquiring the luminancedistribution of the input image data in the determined intermediateluminance region in each image frame; a determining section determiningan input/output characteristic line in each image frame by adaptivelychanging a predetermined reference input/output characteristic line onthe basis of the acquired luminance distribution of the intermediateluminance region, the input/output characteristic line defining thesubstance of image correction on the input image data; a correctionexecuting section executing image correction on the input image data onthe basis of the determined input/output characteristic line; and adisplay section displaying an image on the basis of the input image dataon which image correction is performed.
 14. The image correction circuitaccording to claim 1, wherein the determining means adaptively changesthe predetermined reference input/output characteristic line byadjusting a gain based on a plurality of threshold values such that in acase where the luminance distribution is larger than a first thresholdvalue of the plurality of threshold values, the gain is limited to asubstantially uniform value.
 15. The image correction circuit accordingto claim 1, wherein the weighted luminance center is calculated for theluminance distribution which includes all peaks of the input image datain each entire image frame, and the peaks correspond to a background anda foreground in each entire image frame.
 16. The image correctioncircuit according to claim 1, wherein a size of the black-side luminanceregion is different from a size of the white-side luminance region. 17.The image correction circuit according to claim 2, wherein the firstwidth is equal to three gray levels.